Photoabsorber Modification And Interface Regulation For Efficient And Stable Perovskite Solar Cells

Perovskite solar cells（PSCs）have attracted arising attentions in the demon of photovoltaic technology and their power conversion efficiencies（PCE）have climbed up to 25.8%from initial 3.8%in the past decade,comparable to that of commercial photovoltaic technologies.However,many researchers have demonstrated that the degradation of perovskite films is a complex problem involving intrinsic phase stability issues and some environmental factors（e.g.,exposure to moisture,oxygen,light,temperature）,which simultaneously degrade the device.Herein,we have systematically studied the effects of the compositional engineering,crystallization optimization,grain boundaries passivation and interface modification on the surface micromophology and carrier transport of the perovskite films.As a result,the high-quality perovskite films with large grains,smooth surface,and low defect state density are obtained.Eventually,we successfully integrate efficient and stable PSCs.Details of research contents are as follows:（1）We have added guanidinium（GA）cation in the two-step sequent deposition process to optimize the quality of MAPb I₃perovskite films.The large GA substitutes part of MA and occupies the lattice center of the Pb I₆^4-octahedra,enabling the adjustment of the tolerance factor of perovskite.And GA with the two amine groups can form strong H-X bond with the Pb-X framework,consequently leading to more stable lattice.Hence,we successfully prepare the high-quality perovskite films and integrate C-PSCs（ITO/Sn O₂/Perovskite/Carbon）with PCE of 13.32%.In addition,the optimized C-PSCs exhibites significantly improved storage stability in the air environment.（2）NH₄Br has been introduced to form the intermediate phase NH₄Pb I₃and alleviate the disorder of the octahedron in the rich GA perovskite films mentioned above.As a result,the tolerance for the perovskite roughness fluctuation is increased and the risk of appearing voids and pinholes in the perovskite films is reduced.The fabricated C-PSCs delivers a high PCE of16.19%.Furthermore,the NH₄Br-modified devices in ambient air have exhibited extremely excellent stability against O₂/H₂O,heat and sunlight.（3）A multifunctional polymer,polyvinyl alcohol（PVA）,has been incorporated into two-step sequential deposition process to regulate morphological transform of Pb I₂and then obtain the high-quality perovskite films.Wherein,PVA as a scaffold combines with uncoordinated Pb²⁺in the Pb I₂precursor solution through a strong Pb-O interaction,leading to rough Pb I₂.In the second step,the uneven and heterogeneous Pb I₂allows FA/MA permeation and then drives adequate coordination reactions between Pb I₆^4-octahedron and bulky cations.Furthermore,the PVA gathering at grain boundary passivates redundant Pb²⁺by the Pb-O bonding interactions in the final polycrystalline films.Consequently,we have obtained high-quality perovskite films with promoted crystal growth,inhibited voids formation/delamination and thus reduced trap states.The universality and versatility of this strategy not only enables improved PCEs of 22.81%（Ag-based devices）and 16.58%（carbon-based devices）across architectures but also remarkedly enhances the device stability in ambient-air aging condition,which delivers a facile and broadly applicable additive synergetic strategy for efficient and stable PSCs.（4）Here we demonstrate the use of 3-iodopropyl trimethoxysilane（IDMS）with terminal iodine as an optimized interface modifier to improve optoelectronic properties and suppress trap-state density of the flexible C-PSCs.Benefitting from the supramolecular passivation and energy band adjustment effect of IDMS,flexible C-PSCs after interface modification achieve an PCE of 14.39%with improved carrier mobility.And PCE of the devices maintains more than 80%of the initial value after 2000 bending cycles（R=3.5 mm）.Meanwhile,the hydrophobic film surface enables excellent stability of devices in ambient-air condition.